1. Field of the Invention
The present invention relates to the automated suppression of externally originated structural fires, particularly for structures exposed to wildfire, and more particularly to a fire suppression/protection method and system which employs a two-phase process to enhance efficacy in suppressing the ignition of the structure during its exposure to an external conflagration.
2. Description of the Prior Art
It is well known that certain geographical areas, particularly California, are prone to wildfires which can rage through inhabited areas destroying residential and commercial property worth millions of dollars. Wildfires are often ignited by natural phenomena such as by lightening storms or caused by mankind. Once a wildfire is ignited, it creates an environment that requires fuel, oxygen, and suitable temperature conditions to continue to exist. It has been recognized that a structure having a system which could automatically operate to wet the structure during exposure to such a conflagration would have a considerably higher probability of surviving the fire than if the structure were not wetted during its exposure to burning cinders and flames.
Thus, numerous systems have been proposed to provide fire suppression by wetting the structure during its exposure to a wildfire. These prior art fire suppression system have attempted to solve operational problems created by the extremely harsh environment in which they must operate. For example, the availability of water from the public supply main line could be terminated or severely reduced during such a fire. Most of the disclosed systems have been directed to using water sources other than the main water supply provided by the local city or municipality to the structure. These alternate water sources are typically swimming pools, but could also be lakes, wells, tanks, or the like.
Often, the owners or occupants of a structure in a wildfire zone have voluntarily evacuated or been required by authorities to evacuate before the wildfire has reached the threshold of the structure. Further, other fire suppression systems known in the prior art have disclosed remote operation using local sensors and telephone lines to transmit signals. The use of alternate sources of power, such as batteries, has also been disclosed in situations in which the main source of electrical power to the structure has been interrupted.
Typically, combustion of structures during a wildfire can be initiated by the radiant heat generated by the conflagration. This occurs because the radiant heat raises the temperature of the structure to the point that the structure ignites. Of course, external combustion of the structure can also be initiated by direct contact with the fire. Often, the ignition of the structural fire occurs internally. Generally, this occurs when the internal air temperature of the structure exceeds the external ambient temperature. As the temperature inside the structure increases, the internal air becomes less dense and rises. This situation creates a partial vacuum inside the structure causing heated ambient air carrying fire embers outside of the structure to travel inside through the eves of the structure. Thus, the fire typically ignites in the attic of the structure.
Virtually none of the external fire suppression systems heretofore disclosed in the prior art has achieved commercial success. The reasons for the lack of commercial success are as follows. First, it is not a simple matter to design an external fire suppression system that provides wetting coverage of a residence or other structure that is effective in suppressing ignition of the structure while being assailed by the firestorm associated with a wildfire. The heat of such fires and the associated thermal vortex will combine with preexisting hot, dry winds to knock down or severely degrade the throw patterns of sprinkler heads as disclosed in numerous prior art systems. The maintenance of these throw patterns during such conditions is critical to achieving a complete and effective wetting of the surface area of the structure. Moreover, the high winds and temperatures will rapidly evaporate the water from the surface of the structure, thus further adding to the extreme difficulty in maintaining a complete and continuous (i.e., effective) wetting of the entire surface area of the structure.
Second, the extremely high temperatures can, often cause the internal temperature of the structure to rise to a level such that items within the structure will spontaneously combust, even though the outside of the structure has not been ignited. Third, and perhaps most importantly, the thermal effects of a wildfire will create a high pressure envelope around the outside of the structure relative to that inside the structure, which often leads to a rush of hot dry air into the structure bearing flames and hot embers which can ignite the flammable contents of the structure.
None of the prior art fire suppression system designs heretofore disclosed has addressed the above-noted phenomenon. Thus, there is still a need for a fire suppression and protection system which can solve the foregoing problems presented by the severe conditions under which the system must operate.